Yorgia: Difference between revisions
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'''''Yorgia waggoneri''''' is an [[extinction|extinct]] species from the [[Ediacaran]] period. It had bilateral symmetry, was segmented, and roughly egg shaped. It reached a maximum size of 25 cm across. |
'''''Yorgia waggoneri''''' is an [[extinction|extinct]] species from the [[Ediacaran]] period. It had bilateral symmetry, was segmented, and roughly egg shaped. It reached a maximum size of 25 cm across. |
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[[Trace fossil|Trail]]s made by ''Yorgia'' have been found.<ref name=Ivantsov2002>{{cite journal |
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| author = Ivantsov, A.Y. |
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| coauthors = Malakhovskaya, Y.E. |
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| year = 2002 |
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| title = Giant Traces of Vendian Animals |
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| journal = Doklady Earth Sciences |
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| volume = 385 |
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| issue = 6 |
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| pages = 618–622 |
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| url = http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf |
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| accessdate = 2008-02-24 |
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}}</ref> The trail consists of repeated oval shapes of the fine details of the segmented pattern of the ventral side. The longest recorded trail is 4.3 meters long. It is positive on the lower bed surface. |
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Each oval impression is called a ''platform''. The platforms make a chain, and can overlap each other.<ref name=Ivantsov2002>{{cite journal |
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| author = Ivantsov, A.Y. |
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| coauthors = Malakhovskaya, Y.E. |
|||
| year = 2002 |
|||
| title = Giant Traces of Vendian Animals |
|||
| journal = Doklady Earth Sciences |
|||
| volume = 385 |
|||
| issue = 6 |
|||
| pages = 618–622 |
|||
| url = http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf |
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| accessdate = 2008-02-24 |
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}}</ref> |
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One tentative interpretation is that ''Yorgia'' produced abundant mucus whilst gliding. The mucus sealed the mud bed surface and cemented it so that it was not eroded by subsequent currents. |
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''Yorgia'' would have fed using [[cilia]] in its grooves. This would sweep [[bacteria]] towards the central groove, where more cilia would have swept the microorganisms to its mouth. |
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Another interpretation is that the marks are due to a death roll. |
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However, our current understanding of the [[taphonomy]] and behaviour of microbial mats is insufficient to thoroughly understand these enigmatic traces. |
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Other ''Yorgia'' fossils show internal structure in the original organism, showing two symmetrical rows of nodules, a central tube, rib like tubes, and a semicircular shape with a hole in the circle centre positioned towards the head end. This structure probably is the impression of gonads, intestine and mouth. |
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==References== |
==References== |
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Revision as of 15:24, 8 July 2008
| Yorgia Temporal range: Ediacaran
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| File:Praecambridium Yorgia.jpg | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | Cephalozoa
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| Family: | Yorgiidae
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| Genus: | Yorgia
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| Species: | Y. waggoneri
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| Binomial name | |
| Yorgia waggoneri Ivantsov 1999
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Yorgia waggoneri is a member of the Ediacara biota, which resembles the organisms Dickinsonia and Spriggina. It has a low body consisting of a short wide head and a long body region. Yorgia reached a maximum size of 25 cm across.
The body plan of the Yorgia and other proarticulates is unusual for solitary (non-colonial) metazoans. These bilateral organisms have a segmented metameric body, but, left and right segments (isomers) are organized in an alternating pattern relatively to the axis of the body – they are not direct mirror images. This phenomenon is described as the symmetry of gliding reflection. Some proarticulates demonstrate obvious asymmetry of left and right parts of the body. Yorgia’s initial right isomer is the only one which spreads far towards the left side of the body.
Most body imprints of Yorgia waggoneri have in the past been primarily preserved on the sole of sandstone beds in negative relief. However, some fossils appear as chains of positive imprints with the negative imprint of this animal at the end of the trail. Positive imprints are confined to the “elephant skin” surface texture that is interpreted as the remains of a microbial film. Positive body imprints are interpreted as the feeding tracks produced by an animal working on the surface of a bacterial film. Grazing of that bacterial film could have been accomplished by the work of numerous hair-like organs located on the ventral side of the body. Presumable traces of this work are preserved in the positive imprints as a >>>>-like microrelief.
Taphonomic details revealed in Yorgia due to its large size allow interpretation of the chains of positive imprints of other proarticulates as grazing traces. In addition to Yorgia, two fossil taxa, Epibaion and Phyllozoon, seem to have produced similar grazing traces. Small groups of positive body imprints are documented for Dickinsonia costata as well and Dickinsonia cf. tenuis.
Imprints of the Yorgia waggoneri has been found in the rocks of Vendian period (Ediacaran) White sea region of Russia, dated around 555.5 Ma. and Yorgia sp. has been found in the Central Urals of Russia and Flinders Ranges, Australia.
Yorgia waggoneri is an extinct species from the Ediacaran period. It had bilateral symmetry, was segmented, and roughly egg shaped. It reached a maximum size of 25 cm across.
References
Dzik, Jerzy (2003). "Anatomical Information Content in the Ediacaran Fossils and Their Possible Zoological Affinities". Integrative and Comparative Biology. 43 (1): 114–126. doi:10.1093/icb/43.1.114.